说明：  在做项目（工程）的时候，我们经常要用到比较多的按键，而且IO资源紧张，于是我们就想方设法地在别的模块中节省IO口，好不容易挤出一两个IO口，却发现仍然不够用，实在没办法了就添加一个IC来扫键。一个IC虽然价格不高，但对于大批量生产而且产品利润低的厂家来说，这是一笔不菲的开支! 那，我们能不能想到比较好的扫键方法：用最少的IO口，扫最多的键？可以吗？
(Doing the project (engineering), we often use to a relatively large number of keys, and IO resources, then we will find ways to save in another module I IO, 12 IO hard I squeezed, they found still not enough, it can not add an IC on the button to scan. Although the price of an IC is not high, but high-volume production and product manufacturers with low profits, it is spending a lot of money! It, we can not think of a better way to scan key: with a minimum of IO I, So Most of the key? Can we do that?)